I heard the Messenger of Allah ﷺ say regarding these two verses, "Allah, there is no god but He, the Living, the Sustainer of all existence" [Baqarah 2:255] and "Alif Lam Mim. Allah, there is no god but He, the Living, the Sustainer of all existence" [Aal Imran 3:1–2], "Within them is the Greatest Name of Allah."
سمعت رسول الله ﷺ يقول: في هذه الآيتين {الله لا إله إلا هو الحي القيوم} [البقرة: ٢٥٥] و{الم الله لا إله إلا هو الحي القيوم} [آل عمران: ٢] إن فيهما اسم الله الأعظم.
Ahmad (27611) narrated it from Muhammad bin Bakr, who said, Ubaydullah bin Abu Ziyad informed us, he said, Shahr bin Hawshab narrated to us, from Asma bint Yazid, and he mentioned it.Abu Dawud (1496), Tirmidhi (3478), and Ibn Majah (3855) all narrated it through various chains from Isa bin Yunus, from Ubaydullah bin Abu Ziyad Qaddah, in a similar wording, but in their versions the verse is "and your god is one God" [Baqarah 2:163] instead of "Allah, there is no god but Him, the Living, the Sustainer" [Baqarah 2:255]. Tirmidhi said, This is a hasan sahih hadith.I say, its chain is hasan on account of Shahr bin Hawshab and Ubaydullah bin Abu Ziyad Qaddah, for their hadiths are hasan so long as no error on their part has been established.As for what has been narrated from Ayesha, who said, I heard the Messenger of Allah say, "O Allah, I ask You by Your pure, good, blessed name, most beloved to You, which, when called upon by it, You answer, and when asked by it, You give, and when mercy is sought by it, You show mercy, and when relief is sought by it, You grant relief." She said, and one day he said, "O Ayesha, do you know that Allah has directed me to the name which, when called upon by it, He answers?" She said, so I said, "O Messenger of Allah, by my father and mother, teach it to me." He said, "It is not proper for you, O Ayesha." She said, so I withdrew and sat for a while, then I got up and kissed his head, then I said, "O Messenger of Allah, teach it to me." He said, "It is not proper for me to teach it to you, O Ayesha, it is not proper for you to ask by it for anything of this world." She said, so I got up and performed wudu, then I prayed two units of prayer, then I said, "O Allah, I call upon You as Allah, and I call upon You as the Merciful, and I call upon You as the Righteous, the Compassionate, and I call upon You by all Your beautiful names, those I know of them and those I do not know, to forgive me and have mercy on me." She said, so the Messenger of Allah laughed, then said, "It is indeed among the names by which you called."Its chain is not sahih. Ibn Majah (3859) narrated it from Abu Yusuf the pharmacist, Muhammad bin Ahmad Raqqi. Muhammad bin Salama narrated to us, from Fazari, from Abu Shayba, from Abdullah bin Ukaym Juhani, from Ayesha, and he mentioned it, and its chain is daif on account of the unknown status of Abu Shayba.